A thin film for current collectors and its preparation method

Abstract

This invention relates to the field of current collectors for lithium batteries, and particularly to a thin film for current collectors and its preparation method. The thin film comprises a substrate layer and a modified layer. The substrate layer has two opposing surfaces along its thickness direction, and the modified layer is disposed on the two surfaces. The substrate layer, by weight, comprises 1-20 parts of a conductive agent, 1-10 parts of a coupling agent, 0.1-5 parts of a nucleating agent, and 70-110 parts of a substrate polymer. The modified layer, by weight, comprises 1-20 parts of an anti-sticking masterbatch, 1-20 parts of an adhesion-enhancing masterbatch, 1-20 parts of a conductive agent, 1-10 parts of a coupling agent, and 50-110 parts of a substrate polymer. The current collector thin film provided by this invention exhibits excellent electron transport capability, improves film surface adhesion, conductivity, and tensile properties, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of current collector technology for lithium batteries, and particularly to a thin film for current collectors and its preparation method. Technical Background

[0002] A current collector is a structure or component that collects current and is an indispensable element in lithium-ion batteries. Its main function is to collect and output the current generated by the active material and input the electrode current to the active material, which helps reduce the internal resistance of lithium-ion batteries and improve their coulombic efficiency, cycle stability, and rate performance. Early current collectors in lithium-ion batteries mainly referred to metal foils (such as copper and aluminum foil), which had drawbacks in terms of thickness, weight, and low safety. With the development of new energy lithium battery technology, the processing thickness of traditional negative electrode current collectors (pure copper foil) is nearing its limit, making it difficult to meet the further development of lithium battery technology. Therefore, in recent years, composite current collectors based on polymer films have received widespread attention and application in the new energy industry. Currently, composite current collectors use PET or PP as the substrate. A metal layer of approximately 20-80 nm is first deposited on the surface of a 4-10 μm thick plastic film using vacuum deposition (magnetron sputtering) to metallize the film. Then, an aqueous electroplating process is used to thicken the copper layer to 1-5 μm. The overall thickness of the composite current collector is between 5-15 μm, replacing traditional copper foil. Composite current collectors can save about half the copper, significantly reducing material costs and allowing for further cost reduction in battery cells after mass production. Furthermore, the polymer film used as the base layer of the composite current collector has high tensile strength, soft texture, low coefficient of thermal expansion, and thermal shrinkage characteristics. These features reduce the risk of internal overheating, short circuits, combustion, or explosion when the composite current collector is used in batteries.

[0003] However, current composite current collectors also have shortcomings: 1. The production process is relatively complex, requiring a two-step process to form, namely magnetron sputtering + electroplating, which increases equipment investment and production costs and reduces production efficiency; 2. When the magnetron sputtering process is combined with the base film (PP, PET), the particles may sputter and melt through the base film to form through holes when deposited under high speed and high temperature conditions; 3. The current collector prepared in this way can be regarded as a three-layer composite structure (single-sided), namely the base film layer, the magnetron sputtering layer and the electroplating layer. Due to the weak bonding force between the base film layer and the metal layer, the metal layer is prone to peeling off during use. Summary of the Invention

[0004] To address the problems mentioned in the background art, the present invention provides a current collector film and its preparation method, which is achieved through the following technical solution: A current collector film, the film comprising a substrate layer and a modified layer, the substrate layer having two surfaces opposite each other along the thickness direction, the modified layer being disposed on the two surfaces; the substrate layer, by weight, comprises 1-20 parts of conductive agent, 1-10 parts of coupling agent, 0.1-5 parts of nucleating agent, and 70-110 parts of substrate polymer; the modified layer, by weight, comprises 1-20 parts of anti-sticking masterbatch, 1-20 parts of adhesion performance improving masterbatch, 1-20 parts of conductive agent, 1-10 parts of coupling agent, and 50-110 parts of substrate polymer.

[0005] The inventors discovered that the thin-film substrates in existing current collector technologies lack electrical conductivity, making direct electroplating on the substrate ineffective (electroplating can only be performed on materials with good electrical conductivity). Therefore, existing technologies first vapor-deposit a layer of copper onto the substrate film, and then thicken the copper layer through electroplating. This process, involving magnetron sputtering and electroplating, is complex, inefficient, and costly, resulting in poor interlayer bonding, weak electron transport capability in the finished current collector, and poor uniformity of the copper.

[0006] Therefore, this invention designs a three-layer composite thin film structure. By adding a conductive agent to the film, the insulating film in the prior art becomes a film with good conductivity, which can be directly electroplated. This improves production efficiency and reduces costs. At the same time, the bonding strength between the metal layers is high and the metal layers are uniform, with better electron transport capability.

[0007] Adding adhesion-enhancing masterbatch to the modified layer of the film, the interfacial adhesion enhancer in the masterbatch contains abundant polar functional groups, which can effectively enhance the polarity of the film surface, thereby increasing the surface tension of the film and promoting the adhesion performance of the film surface, thus improving the adhesion between the film and the metal layer.

[0008] Furthermore, the bonding performance improving masterbatch is composed of a base polymer, an interfacial bonding improver, and other additives in a mass ratio of (35-90):(5-35):(5-30).

[0009] Furthermore, the anti-sticking masterbatch is composed of a lubricant, an opening agent, and a base polymer in a mass ratio of (1-10):(1-20):(70-98);

[0010] Preferably, the lubricant is one or more of oleamide, erucamide, PE wax, and silicone oil;

[0011] Preferably, the opening agent is one or more of calcium carbonate, diatomaceous earth, talc, silica, and organosilicon microspheres;

[0012] The preferred method for preparing the anti-sticking masterbatch is as follows: the raw materials are fed into a high-speed mixer for mixing, and then melt-extruded, stretched, cooled, pelletized and dried by a twin-screw extruder at a temperature of 180-260°C.

[0013] Furthermore, the substrate polymer includes one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyimide, polyethylene, polypropylene, and polyvinyl chloride.

[0014] Furthermore, the substrate layer, by weight, comprises 1 to 10 parts of conductive agent, 1 to 5 parts of coupling agent, 0.1 to 3 parts of nucleating agent, and 82 to 97.9 parts of homopolymer polypropylene; the modified layer, by weight, comprises 1 to 8 parts of anti-sticking masterbatch, 1 to 10 parts of adhesion performance improving masterbatch, 1 to 10 parts of conductive agent, 1 to 5 parts of coupling agent, and 67 to 96 parts of copolymer polypropylene.

[0015] Furthermore, the interfacial adhesion enhancer is one or more of ethylene glycol polyoxyethylene ether, 2,2,2-trifluoroethyl methacrylate, N,N′-methylenediacrylamide, and p-hydroxybenzoic acid hydrazide.

[0016] Furthermore, the other additives include stearate-esterified hyperbranched polyamide esters, carboxyl-terminated hyperbranched polyesters, and tetra(2,4-di-tert-butyl-4,4'-bisphosphonates.

[0017] The preferred mass ratio of the stearate-esterified hyperbranched polyamide ester, the carboxyl-terminated hyperbranched polyester, and the tetra(2,4-di-tert-butyl-4,4'-bi)bisphosphonate is (15-60):(35-84.9):(0.1-5).

[0018] The preferred method for preparing the stearate-esterified hyperbranched polyamide ester is as follows: 40-60 parts by weight of succinic anhydride and 60-40 parts by weight of diethanolamine are added to 80-180 parts by weight of N,N-dimethylformamide, and stirred for 1-5 hours at a temperature of 20-50°C and a speed of 200-600 rpm. Then, 0.1-5 parts by weight of p-toluenesulfonic acid and 0.5-30 parts by weight of toluene are added, stirring is continued, and heating begins. Water produced during the reaction is separated under reduced pressure until no water droplets are produced, at which point the reaction is terminated to obtain prepolymer A. 0.5-30 parts by weight of stearic acid are added to prepolymer A, and stirring is continued at a speed of 100-300 rpm to carry out the esterification reaction until no water droplets are generated. Excess N,N-dimethylformamide, toluene, and small molecules are distilled off under reduced pressure to obtain the stearate-esterified hyperbranched polyamide ester.

[0019] Among them, stearate-esterified hyperbranched polyamide ester and carboxyl-terminated hyperbranched polyester are hyperbranched polymers. Hyperbranched polymers have a dense branched structure, which is beneficial to improve adhesion. In addition, these two polymers contain polar groups such as amide groups, ester groups, hydroxyl groups and carboxyl groups, which can also ultimately improve the adhesion between the film and the metal layer.

[0020] Polypropylene is a non-polar polymer. When it undergoes surface treatment, its corona value will significantly decrease over time. However, tetrakis(2,4-di-tert-butyl-4,4'-bi)bisphosphonate in the adhesive performance enhancement masterbatch has a special function: it can lock the corona value and effectively slow down the decay of the corona, thus ensuring the strength of the bond.

[0021] The preferred method for preparing the adhesive performance-enhancing masterbatch is as follows: the raw materials are fed into a high-speed mixer for mixing, and then melt-extruded, stretched, cooled, pelletized and dried by a twin-screw extruder at a temperature of 180-260°C.

[0022] Furthermore, the conductive agent is composed of nano-sized antimony-doped tin oxide powder and single-walled carbon nanotubes in a mass ratio of (20-50):(50-80);

[0023] The components in the conductive agent, after biaxial stretching, cause the single-walled carbon nanotubes to separate and align in the matrix, which can improve the mechanical properties of the film.

[0024] Preferably, the coupling agent is one or more selected from γ-aminopropyltriethoxysilane, γ-ureopropyltriethoxysilane, and 3-(2,3-epoxypropoxy)propyltrimethoxysilane;

[0025] Preferably, the nucleating agent is one or more of dimethicone (DBS) and its derivatives, aromatic phosphate salts, and substituted benzoates.

[0026] Furthermore, the thickness of the current collector film is 4–15 μm; wherein the thickness of the substrate layer is 2–13 μm and the thickness of the modified layer is 1–4 μm.

[0027] The present invention also provides a method for preparing a current collector thin film according to the above, comprising the following steps:

[0028] S1, Melt Extrusion

[0029] According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 180-260°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt.

[0030] S2, Casting

[0031] The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 80-300 μm and the temperature of the cooling drum is 6-30°C.

[0032] S3, Biaxial tension

[0033] The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 100-150℃, the stretching temperature is 120-160℃, the longitudinal stretching ratio is 4-8 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 110-155℃, the stretching temperature is 130-170℃, the stretching ratio is 5-9 times, the heat setting temperature is 150-175℃, and the heat setting time is 1-50 seconds to obtain a film.

[0034] S4. Rewinding

[0035] The film obtained in step S4 is cooled by air in the platform area and then subjected to corona treatment by the traction system. The corona treatment power is 4-18 Wmin / m. 2 Then it enters the winding system to wind the film, with a winding tension of 10-80 N / m.

[0036] S5, Slicing

[0037] The wound film is cut as required to obtain the current collector film with a thickness of 4-15 μm.

[0038] The present invention adopts the above technical solution and has the following advantages compared with the prior art:

[0039] The present invention provides a current collector film and its preparation method. Through reasonable formulation design and film layer structure design, the expected function of the film is realized, thus providing a biaxially oriented polypropylene film with excellent comprehensive performance, easy processing, good conductivity, and enhanced composite adhesion. Testing shows that the film has significantly improved surface tension, reduced resistivity, adhesion strength > 5.0 N, longitudinal tensile strength > 175 MPa, and transverse tensile strength > 275 MPa. Furthermore, when an abnormal short circuit occurs in the battery, the conductive base film melts and fractures upon heating, preventing combustion caused by continuous short circuits and ensuring battery safety. This film has wide applications, outstanding performance, is easy to process, has a simple production process, high production efficiency, and is easily industrialized, showing great market application prospects. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 A thin film structure diagram for current collectors provided by the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention provides a thin film for current collectors, the solution of which is as follows:

[0044] like Figure 1 As shown, the film includes a substrate layer 10 and a modified layer 20. The substrate layer 10 has two surfaces opposite each other along the thickness direction, and the modified layer 20 is disposed on the two surfaces. The substrate layer, by weight, includes 1-20 parts of conductive agent, 1-10 parts of coupling agent, 0.1-5 parts of nucleating agent, and 70-110 parts of substrate polymer. The modified layer, by weight, includes 1-20 parts of anti-sticking masterbatch, 1-20 parts of adhesion-enhancing masterbatch, 1-20 parts of conductive agent, 1-10 parts of coupling agent, and 50-110 parts of substrate polymer.

[0045] The bonding performance improving masterbatch is composed of a base polymer, an interfacial bonding improver, and other additives in a mass ratio of (35-90):(5-35):(5-30).

[0046] Other additives include stearate-esterified hyperbranched polyamide esters, carboxyl-terminated hyperbranched polyesters, and tetra(2,4-di-tert-butyl-4,4'-bisphosphonates.

[0047] The preparation method of stearate-esterified hyperbranched polyamide ester is as follows: 40-60 parts by weight of succinic anhydride and 60-40 parts by weight of diethanolamine are placed in a reaction vessel, and 80-180 parts by weight of N,N-dimethylformamide are added. The mixture is stirred for 1-5 hours at a temperature of 20-50℃ and a speed of 200-600 rpm. Then, 0.1-5 parts by weight of p-toluenesulfonic acid and 0.5-30 parts by weight of toluene are added to the reaction vessel, and the mixture is stirred and heated. The stirring is continued at 200-500 rpm, and the water produced in the reaction is separated under reduced pressure until no water droplets are produced. The reaction is then stopped to obtain prepolymer A. 0.5-30 parts by weight of stearic acid are added to prepolymer A, and the mixture is stirred at 100-300 rpm to carry out the esterification reaction until no water droplets are generated. The excess N,N-dimethylformamide, toluene, and small molecules are distilled off under reduced pressure to obtain stearate-esterified hyperbranched polyamide ester.

[0048] The anti-sticking masterbatch is composed of lubricant, opening agent and base polymer in a mass ratio of (1-10):(1-20):(70-98);

[0049] The thickness of the current collector film is 4–15 μm, wherein the thickness of the substrate layer is 2–13 μm and the thickness of the modified layer is 1–4 μm.

[0050] The present invention also provides an operational example of the method for preparing the thin film for current collector, the steps of which are as follows:

[0051] S1, Melt Extrusion

[0052] According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 180-260°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt.

[0053] S2, Casting

[0054] The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 80-300 μm and the temperature of the cooling drum is 6-30°C.

[0055] S3, Biaxial tension

[0056] The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 100-150℃, the stretching temperature is 120-160℃, the longitudinal stretching ratio is 4-8 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 110-155℃, the stretching temperature is 130-170℃, the stretching ratio is 5-9 times, the heat setting temperature is 150-175℃, and the heat setting time is 1-50 seconds to obtain a film.

[0057] S4. Rewinding

[0058] The film obtained in step S4 is cooled by air in the platform area and then subjected to corona treatment by the traction system. The corona treatment power is 4-18 Wmin / m. 2 Then it enters the winding system to wind the film, with a winding tension of 10-80 N / m.

[0059] S5, Slicing

[0060] The wound film is cut as required to obtain the current collector film with a thickness of 4-15 μm.

[0061] The present invention also provides the following embodiments and comparative examples:

[0062] Example 1

[0063] A current collector film, wherein the substrate layer comprises, by weight, 5 parts conductive agent, 1.5 parts coupling agent, 0.5 parts nucleating agent and 83 parts homopolymer polypropylene; and the modified layer comprises, by weight, 3 parts anti-sticking masterbatch, 3 parts adhesion performance improving masterbatch, 5 parts conductive agent, 1.5 parts coupling agent and 87.5 parts copolymer polypropylene.

[0064] The bonding performance improving masterbatch, by weight percentage, includes 45 wt% polypropylene, 25 wt% interfacial bonding improver and 30 wt% other additives.

[0065] The interfacial adhesion enhancer is a mixture of ethylene glycol polyoxyethylene ether, 2,2,2-trifluoroethyl methacrylate, N,N′-methylenediacrylamide, and p-hydroxybenzoic acid hydrazide in a mass ratio of 1:1:1:1;

[0066] Other additives are stearate-esterified hyperbranched polyamide ester, carboxyl-terminated hyperbranched polyester, and tetra(2,4-di-tert-butyl-4,4'-bi)bisphosphonate mixed in a mass ratio of 30:68:2;

[0067] The preparation method of stearate-esterified hyperbranched polyamide ester is as follows: 60 parts by weight of succinic anhydride and 40 parts by weight of diethanolamine are added to 160 parts by weight of N,N-dimethylformamide, and stirred for 3 hours at 50°C and 600 rpm. Then, 4 parts by weight of p-toluenesulfonic acid and 25 parts by weight of toluene are added, stirring is continued and heating is started, and the water produced by the reaction is separated under reduced pressure until no water droplets are produced, at which point the reaction is stopped to obtain prepolymer A. 15 parts by weight of stearic acid are added to prepolymer A, and stirring is continued at 300 rpm to carry out the esterification reaction until no water droplets are generated. Excess N,N-dimethylformamide, toluene, and small molecules are distilled off under reduced pressure to obtain stearate-esterified hyperbranched polyamide ester.

[0068] The conductive agent, by mass percentage, comprises 30 wt% nano-sized antimony-doped tin oxide powder and 70 wt% single-walled carbon nanotubes;

[0069] The coupling agent is 3-(2,3-epoxypropoxy)propyltrimethoxysilane;

[0070] The nucleating agent is dimethicone (DBS);

[0071] The anti-sticking masterbatch, by weight percentage, comprises 5 wt% lubricant, 10 wt% opening agent and 85 wt% copolymer polypropylene;

[0072] The lubricant is erucamide, and the opening agent is silica;

[0073] The thickness of the current collector film is 8 μm; of which, the thickness of the substrate layer is 5 μm and the thickness of the modified layer is 1.5 μm.

[0074] Methods for preparing thin films for current collectors include:

[0075] S1, Melt Extrusion

[0076] According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 215°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt;

[0077] S2, Casting

[0078] The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 240 μm and the temperature of the cooling drum is 20 °C.

[0079] S3, Biaxial tension

[0080] The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 120°C, the stretching temperature is 130°C, the longitudinal stretching ratio is 5 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 135°C, the stretching temperature is 155°C, the stretching ratio is 6 times, the heat setting temperature is 166°C, and the heat setting time is 8 seconds to obtain a film.

[0081] S4. Rewinding

[0082] The film obtained in step S4 is cooled by air in the platform area and then subjected to corona treatment by the traction system. The corona treatment power is 12 W / min / m. 2 Then it enters the winding system to wind the film, with a winding tension of 40 N / m;

[0083] S5, Slicing

[0084] The wound film is cut as required to obtain the current collector film with a thickness of 8 μm.

[0085] Example 2

[0086] Compared with Example 1, the difference of this example is:

[0087] The substrate layer, by weight, comprises 6 parts conductive agent, 1.5 parts coupling agent, 0.5 parts nucleating agent, and 92 parts homopolymer polypropylene; the modified layer, by weight, comprises 4 parts anti-sticking masterbatch, 6 parts adhesion performance improving masterbatch, 6 parts conductive agent, 1.5 parts coupling agent, and 82.5 parts copolymer polypropylene.

[0088] The bonding performance improving masterbatch, by weight percentage, includes 90 wt% polypropylene, 5 wt% interfacial bonding improver and 5 wt% other additives.

[0089] The interfacial adhesion enhancer is ethylene glycol polyoxyethylene ether;

[0090] Other additives are stearate-esterified hyperbranched polyamide ester, carboxyl-terminated hyperbranched polyester, and tetra(2,4-di-tert-butyl-4,4'-diphosphonate) bisphosphonates mixed in a mass ratio of 60:35:5;

[0091] The conductive agent, by mass percentage, comprises 20 wt% nano-sized antimony-doped tin oxide powder and 80 wt% single-walled carbon nanotubes;

[0092] The coupling agent is γ-aminopropyltriethoxysilane;

[0093] Nucleating agents are aromatic phosphate salts;

[0094] The anti-sticking masterbatch, by weight percentage, comprises 1 wt% lubricant, 1 wt% opening agent, and 98 wt% copolymer polypropylene;

[0095] The lubricant is silicone oil, and the opening agent is calcium carbonate;

[0096] The thickness of the current collector film is 4 μm; of which, the thickness of the substrate layer is 2 μm and the thickness of the modified layer is 1 μm.

[0097] Methods for preparing thin films for current collectors include:

[0098] S1, Melt Extrusion

[0099] According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 180°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt;

[0100] S2, Casting

[0101] The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 80 μm and the temperature of the cooling drum is 6 °C.

[0102] S3, Biaxial tension

[0103] The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 110°C, the stretching temperature is 130°C, the longitudinal stretching ratio is 5.5 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 135°C, the stretching temperature is 150°C, the stretching ratio is 6.5 times, the heat setting temperature is 165°C, and the setting time is 10 seconds to obtain a film.

[0104] S4. Rewinding

[0105] The film obtained in step S4 is cooled by air in the platform area and then subjected to corona treatment by the traction system. The corona treatment power is 4 W / min / m. 2 Then it enters the winding system to wind the film, with a winding tension of 10 N / m;

[0106] S5, Slicing

[0107] The wound film is cut as required to obtain the current collector film with a thickness of 4 μm.

[0108] Except for the differences mentioned above, everything else is the same as in Example 1.

[0109] Example 3

[0110] Compared with Example 1, the difference of this example is:

[0111] The substrate layer, by weight, comprises 1 part conductive agent, 1 part coupling agent, 0.1 part nucleating agent, and 97.9 parts homopolymer polypropylene; the modified layer, by weight, comprises 1 part anti-sticking masterbatch, 1 part adhesion performance improving masterbatch, 1 part conductive agent, 1 part coupling agent, and 96 parts copolymer polypropylene.

[0112] The bonding performance improving masterbatch, by weight percentage, includes 35 wt% polypropylene, 35 wt% interfacial bonding improver and 30 wt% other additives.

[0113] The interfacial adhesion enhancer is p-hydroxybenzoic acid hydrazide;

[0114] Other additives are stearate-esterified hyperbranched polyamide ester, carboxyl-terminated hyperbranched polyester, and tetra(2,4-di-tert-butyl-4,4'-diphosphonate) bisphosphonates mixed in a mass ratio of 15:84.9:0.1;

[0115] The conductive agent, by mass percentage, comprises 50 wt% nano-sized antimony-doped tin oxide powder and 50 wt% single-walled carbon nanotubes;

[0116] The coupling agent is γ-ureopropyltriethoxysilane;

[0117] The nucleating agent is a substituted benzoate;

[0118] The anti-sticking masterbatch, by weight percentage, comprises 10 wt% lubricant, 20 wt% opening agent, and 70 wt% copolymer polypropylene;

[0119] The lubricant is PE wax, and the opening agent is silicone microspheres;

[0120] The thickness of the current collector film is 15 μm; of which, the thickness of the substrate layer is 13 μm and the thickness of the modified layer is 1 μm.

[0121] Methods for preparing thin films for current collectors include:

[0122] S1, Melt Extrusion

[0123] According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 260°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt;

[0124] S2, Casting

[0125] The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 300 μm and the temperature of the cooling drum is 30°C.

[0126] S3, Biaxial tension

[0127] The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 150°C, the stretching temperature is 160°C, the longitudinal stretching ratio is 8 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 155°C, the stretching temperature is 170°C, the stretching ratio is 9 times, the heat setting temperature is 175°C, and the heat setting time is 50 seconds to obtain a film.

[0128] S4. Rewinding

[0129] The film obtained in step S4 is cooled by air in the platform area and then subjected to corona treatment by the traction system. The corona treatment power is 18 W / min / m. 2 Then it enters the winding system to wind the film, with a winding tension of 80 N / m;

[0130] S5, Slicing

[0131] The wound film is cut as required to obtain the current collector film with a thickness of 15 μm.

[0132] Except for the differences mentioned above, everything else is the same as in Example 1.

[0133] Comparative Example 1

[0134] Compared to Example 1, the difference in this comparative example is:

[0135] The substrate layer is homopolymer polypropylene; the modified layer, by weight, includes 3 parts anti-sticking masterbatch and 97 parts copolymer polypropylene.

[0136] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0137] Comparative Example 2

[0138] Compared to Example 1, the difference in this comparative example is:

[0139] The substrate layer, by weight, comprises 5 parts conductive agent, 1.5 parts coupling agent, 0.5 parts nucleating agent, and 83 parts homopolymer polypropylene; the modified layer, by weight, comprises 3 parts anti-sticking masterbatch, 5 parts conductive agent, 1.5 parts coupling agent, and 90.5 parts copolymer polypropylene.

[0140] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0141] Comparative Example 3

[0142] Compared to Example 1, the difference in this comparative example is:

[0143] The substrate layer, by weight, comprises 1.5 parts coupling agent, 0.5 parts nucleating agent, and 88 parts homopolymer polypropylene; the modified layer, by weight, comprises 3 parts anti-sticking masterbatch, 3 parts anti-sticking masterbatch, 1.5 parts coupling agent, and 92.5 parts copolymer polypropylene.

[0144] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0145] Comparative Example 4

[0146] Compared to Example 1, the difference in this comparative example is:

[0147] The adhesive performance enhancement masterbatch, by weight percentage, comprises 70 wt% polypropylene and 30 wt% other additives;

[0148] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0149] Comparative Example 5

[0150] Compared to Example 1, the difference in this comparative example is:

[0151] The bonding performance improving masterbatch, by weight percentage, comprises 75 wt% polypropylene and 25 wt% interfacial bonding improver;

[0152] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0153] Comparative Example 6

[0154] Compared to Example 1, the difference in this comparative example is:

[0155] The interfacial adhesion enhancer is an oxygen-functionalized polyester (glycerol-modified polyester);

[0156] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0157] Comparative Example 7

[0158] Compared to Example 1, the difference in this comparative example is:

[0159] Other additives are stearate-esterified hyperbranched polyamide esters;

[0160] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0161] Comparative Example 8

[0162] Compared to Example 1, the difference in this comparative example is:

[0163] Other additives are carboxyl-terminated hyperbranched polyesters;

[0164] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0165] Comparative Example 9

[0166] Compared to Example 1, the difference in this comparative example is:

[0167] Other adjuvants include tetra(2,4-di-tert-butyl-4,4'-bisphosphonates);

[0168] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0169] Comparative Example 10

[0170] Compared to Example 1, the difference in this comparative example is:

[0171] Other additives are stearate-esterified hyperbranched polyamide ester, carboxyl-terminated hyperbranched polyester, and tetra(2,4-di-tert-butyl-4,4'-diphosphonate) mixed in a mass ratio of 30:20:50;

[0172] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0173] Comparative Example 11

[0174] Compared to Example 1, the difference in this comparative example is:

[0175] The conductive agent is nano-sized antimony-doped tin oxide powder;

[0176] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0177] Comparative Example 12

[0178] Compared to Example 1, the difference in this comparative example is:

[0179] The conductive agent is single-walled carbon nanotubes;

[0180] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0181] Comparative Example 13

[0182] Compared to Example 1, the difference in this comparative example is:

[0183] The conductive agent is graphene;

[0184] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0185] Comparative Example 14

[0186] Compared to Example 1, the difference in this comparative example is:

[0187] The conductive agent, by mass percentage, comprises 10 wt% nano-sized antimony-doped tin oxide powder and 90 wt% single-walled carbon nanotubes; except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0188] Comparative Example 15

[0189] Compared to Example 1, the difference in this comparative example is:

[0190] The substrate layer, by weight, comprises 5 parts conductive agent, 0.5 parts nucleating agent, and 84.5 parts homopolymer polypropylene; the modified layer, by weight, comprises 3 parts anti-sticking masterbatch, 3 parts adhesion performance improving masterbatch, 5 parts conductive agent, and 89 parts copolymer polypropylene.

[0191] Except for the differences mentioned above, the remaining components and preparation methods are the same as in Example 1.

[0192] The performance of the above embodiments and comparative examples was tested, and the specific results are shown in the table below:

[0193]

[0194] Note:

[0195] (1) Tensile strength test: The test shall be conducted in accordance with the requirements of GB / T 1040.3 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets".

[0196] (2) Surface tension performance test: The test shall be conducted in accordance with the requirements of GB / T 14216 "Determination of wetting tension of plastic films and sheets".

[0197] (3) Adhesion performance test: A layer of Permacel P-94 double-sided tape was adhered to a 1mm thick aluminum foil. A current collector film was adhered on top of the double-sided tape. A layer of ethylene-acrylic acid copolymer film (DuPont Nurcel 0903, 50μm thick) was then covered on top of the current collector film. Then, a 1.3×10⁵ N / m... 2 The sample was hot-pressed at 120℃ for 10 seconds, cooled to room temperature, and cut into strips of 150mm × 15mm. The ethylene-acrylic acid copolymer film of the sample strips was then fixed to the upper clamp of a tensile testing machine, while the rest was fixed to the lower clamp. After fixing, the two were peeled at an angle of 180° and a speed of 100mm / min to test the peel force, i.e., the adhesion force between the polypropylene film and the metal layer.

[0198] (4) Conductivity performance test: The test shall be conducted in accordance with the requirements of GB / T 17473.3 "Test method for precious metal pastes for microelectronics".

[0199] The test results of Examples 1-3 and Comparative Examples 1-15 show that the biaxially oriented polypropylene film for film production produced by the present invention has excellent electrical conductivity and adhesion properties, while maintaining excellent tensile strength, which can meet the needs of different high-end markets.

[0200] The comparison results of Example 1 and Comparative Example 2 show that the adhesion performance enhancement masterbatch in this invention can effectively enhance the polarity of the film surface, thereby increasing the surface tension of the film and promoting the adhesion performance of the film surface. The comparison results of Example 1 and Comparative Examples 4 and 5 show that the interfacial adhesion enhancer and other additives in the adhesion performance enhancement masterbatch work synergistically to better enhance the surface tension and adhesion performance of the film. Among them, Comparative Examples 6-10 show that the selection of interfacial adhesion enhancer and other additives is also crucial: the stearate-esterified hyperbranched polyamide ester and carboxyl-terminated hyperbranched polyester among the other additives are hyperbranched polymers. The hyperbranched polymer structure has a dense branched structure, which is beneficial to improving adhesion. Moreover, these two polymers contain polar groups such as amide groups, ester groups, hydroxyl groups and carboxyl groups, which can also ultimately enhance the adhesion between the film and the metal layer. Tetra(2,4-di-tert-butyl-4,4'-bi)bisphosphonate has a special function. It can lock the corona value and effectively slow down the decay of the corona, thereby ensuring the strength of the bond between the film and the metal layer.

[0201] The comparison results of Example 1 and Comparative Examples 11-14 show that the selection of conductive agent affects the conductivity and tensile strength of the film. The selection of nanoscale antimony-doped tin oxide powder and single-walled carbon nanotubes with a specific mass ratio is beneficial to improving the conductivity and tensile strength of the film.

[0202] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thin film for current collection, characterized in that: The film comprises a substrate layer and a modified layer. The substrate layer has two surfaces opposite each other along the thickness direction, and the modified layer is disposed on the two surfaces. The substrate layer comprises, by weight, 1 to 10 parts of conductive agent, 1 to 5 parts of coupling agent, 0.1 to 3 parts of nucleating agent, and 82 to 97.9 parts of homopolymer polypropylene. The modified layer comprises, by weight, 1 to 8 parts of anti-sticking masterbatch, 1 to 10 parts of adhesion-enhancing masterbatch, 1 to 10 parts of conductive agent, 1 to 5 parts of coupling agent, and 67 to 96 parts of copolymer polypropylene. The bonding performance improving masterbatch is composed of a base polymer, an interfacial bonding improver, and other additives in a mass ratio of (35-90):(5-35):(5-30); The interfacial adhesion enhancer is one or more of the following: ethylene glycol polyoxyethylene ether, 2,2,2-trifluoroethyl methacrylate, N,N′-methylenediacrylamide, and p-hydroxybenzoic acid hydrazide. The other additives are stearate-esterified hyperbranched polyamide ester, carboxyl-terminated hyperbranched polyester, and tetra(2,4-di-tert-butyl-4,4'-bisphosphonate) in a mass ratio of (15-60):(35-84.9):(0.1-5). The preparation method of the stearate-esterified hyperbranched polyamide ester is as follows: 40-60 parts by weight of succinic anhydride and 60-40 parts by weight of diethanolamine are added to 80-180 parts by weight of N,N-dimethylformamide, and stirred for 1-5 hours at a temperature of 20-50°C and a speed of 200-600 rpm; then 0.1-5 parts by weight of p-toluenesulfonic acid and 0.5-30 parts by weight of toluene are added, stirring is continued and heating begins, and the water produced in the reaction is separated under reduced pressure until no water droplets are produced, at which point the reaction is stopped to obtain prepolymer A; 0.5-30 parts by weight of stearic acid are added to prepolymer A, and stirring is continued at a speed of 100-300 rpm to carry out the esterification reaction until no water droplets are generated; excess N,N-dimethylformamide, toluene, and small molecules are distilled off under reduced pressure to obtain the stearate-esterified hyperbranched polyamide ester; The anti-sticking masterbatch is composed of a lubricant, an opening agent, and a substrate polymer in a mass ratio of (1-10):(1-20):(70-98); the lubricant is one or more of oleamide, erucamide, PE wax, and silicone oil; the opening agent is one or more of calcium carbonate, diatomaceous earth, talc, silica, and organosilicon microspheres. The substrate polymer includes one or more of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyimide, polyethylene, polypropylene, and polyvinyl chloride.

2. The current collector film according to claim 1, characterized in that: The conductive agent is composed of nano-sized antimony-doped tin oxide powder and single-walled carbon nanotubes in a mass ratio of (20-50):(50-80); The coupling agent is γ aminopropyltriethoxysilane, γ Uretopropyltriethoxysilane and 3 (2,3) One or more of the following: (epoxypropoxy)propyltrimethoxysilane; The nucleating agent is one or more of dimethicone (DBS) and its derivatives, aromatic phosphate salts, and substituted benzoates.

3. The current collector film according to claim 1, characterized in that: The thickness of the current collector film is 4–15 μm; wherein the thickness of the substrate layer is 2–13 μm and the thickness of the modified layer is 1–4 μm.

4. A method for preparing a current collector thin film according to any one of claims 1-3, characterized in that, Includes the following steps: S1, Melt Extrusion According to a certain weight ratio, the raw materials of the substrate layer and the modified layer are respectively fed into different extruders, melted and plasticized at a temperature of 180-260°C, and extruded, and then flowed into the same coat hanger-shaped die to form a melt; S2, Casting The melt is attached to a cooling drum using a low-pressure air knife to form a thick sheet, wherein the thickness of the sheet is 80-300 μm and the temperature of the cooling drum is 6-30°C. S3, Biaxial tension The thick sheet obtained in step S2 is subjected to asynchronous stretching. First, longitudinal stretching is performed: the preheating temperature is 100-150℃, the stretching temperature is 120-160℃, the longitudinal stretching ratio is 4-8 times, and the longitudinal stretching is cooled to room temperature. Then, transverse stretching is performed: the preheating temperature is 110-155℃, the stretching temperature is 130-170℃, the stretching ratio is 5-9 times, the heat setting temperature is 150-175℃, and the heat setting time is 1-50 seconds to obtain a film. S4. Roll up After the film obtained in step S4 is cooled by air in the platform area, it is subjected to corona treatment by the traction system with a corona treatment power of 4 to 18 Wmin / m², and then enters the winding system for film winding with a winding tension of 10 to 80 N / m. S5, Slicing The wound film is cut as required to obtain the current collector film with a thickness of 4-15 μm.

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